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https://issues.apache.org/jira/browse/LUCENE-1799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12893288#action_12893288
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Robert Muir commented on LUCENE-1799:
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yonik, what were you benchmarking? I think you should benchmark overall
indexing time, of which encode is just a blip (<1% of).
and yes, since the start state is 0x40 the FIRST cjk char is a diff from 0x40,
but any subsequent ones yield savings.
in general you wont get much compression for chinese.. id say max 25%
for russian, arabic, hebrew, japanese it will do a lot better: max 40%
for indian languages you tend to get about 50%.
I also dont know how you encoded word at a time, because i get quite different
results. I focused a lot on 'single-byte diffs' to be fast (e.g. just
subtraction) and I think i do a lot better for english than the 160% described
in http://unicode.org/notes/tn6/
Furthermore, utf-8 is a complete no-op for english, so being a compression
algorithm that is only 29% slower than (byte) char is good in my book, but i
dont measure 29% for english.
I don't think there is any problem in encode speed at all.
> Unicode compression
> -------------------
>
> Key: LUCENE-1799
> URL: https://issues.apache.org/jira/browse/LUCENE-1799
> Project: Lucene - Java
> Issue Type: New Feature
> Components: Store
> Affects Versions: 2.4.1
> Reporter: DM Smith
> Priority: Minor
> Attachments: LUCENE-1779.patch, LUCENE-1799.patch, LUCENE-1799.patch,
> LUCENE-1799.patch, LUCENE-1799.patch, LUCENE-1799.patch, LUCENE-1799.patch,
> LUCENE-1799.patch, LUCENE-1799.patch, LUCENE-1799.patch, LUCENE-1799.patch,
> LUCENE-1799.patch, LUCENE-1799.patch, LUCENE-1799.patch, LUCENE-1799.patch,
> LUCENE-1799_big.patch
>
>
> In lucene-1793, there is the off-topic suggestion to provide compression of
> Unicode data. The motivation was a custom encoding in a Russian analyzer. The
> original supposition was that it provided a more compact index.
> This led to the comment that a different or compressed encoding would be a
> generally useful feature.
> BOCU-1 was suggested as a possibility. This is a patented algorithm by IBM
> with an implementation in ICU. If Lucene provide it's own implementation a
> freely avIlable, royalty-free license would need to be obtained.
> SCSU is another Unicode compression algorithm that could be used.
> An advantage of these methods is that they work on the whole of Unicode. If
> that is not needed an encoding such as iso8859-1 (or whatever covers the
> input) could be used.
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